1. Field of the Invention
The present invention relates to an elastic wave device, an electronic component including an elastic wave device, and a method for manufacturing an elastic wave device.
2. Description of the Related Art
Elastic wave devices serving as duplexers or section filters are incorporated in RF (radio frequency) circuits in communication equipment, e.g., cellular phones.
For example, Japanese Unexamined Patent Application Publication No. 2011-244065 describes an elastic wave device 101, as illustrated in FIG. 8A and FIG. 8B. FIG. 8A is a diagram of the elastic wave device 101 in plan view, and FIG. 8B is a sectional view of the elastic wave device 101 taken along a line VIIIB-VIIIB in FIG. 8A. The elastic wave device 101 includes a piezoelectric substrate 110, an IDT (inter digital transducer) electrode 111, wiring 114, a pad 120, a first dielectric layer 115, and a second dielectric layer 116. The IDT electrode 111 includes first and second comb-shaped electrodes 112 and 113. The first and second comb-shaped electrodes 112 and 113 have a plurality of electrode fingers 112a and 113a, respectively, arranged along the elastic wave propagation direction (Y direction) and busbars 112b and 113b respectively connected to the plurality of electrode fingers 112a and 113a. The electrode fingers 112a and 113a are formed from a first electrically conductive film 141. The busbars 112b and 113b are formed from a multilayer body of the first electrically conductive film 141 and a second electrically conductive film 142.
The IDT electrode 111 of the elastic wave device 101 is disposed on the piezoelectric substrate 110. The first dielectric layer 115 is a layer to adjust a band width ratio of the elastic wave device 101 or to compensate the frequency temperature characteristics and is disposed on the piezoelectric substrate 110 so as to cover the electrode fingers 112a and 113a. The second dielectric layer 116 is a layer to adjust the resonant frequency of the elastic wave device 101 and is disposed so as to cover the first dielectric layer 115. Above the piezoelectric substrate 110, the region in which the second electrically conductive film 142 defining the busbars 112b and 113b and the region in which the second dielectric layer 116 is disposed do not overlap one another and are different regions.
FIG. 8B is a sectional view of a cross-section of part of the elastic wave device 101 taken along a line VIIIB-VIIIB illustrated in FIG. 8A. FIG. 9 is a sectional view of the entire elastic wave device 101 taken along a line IX-IX illustrated in FIG. 8A. The elastic wave device 101 illustrated in FIG. 9 further includes under bump metals 118. The under bump metals 118 are disposed on parts of pads 120. The wiring 114 and the pads 120 are formed from a multilayer body of the first electrically conductive film 141 and the second electrically conductive film 142.
A method for manufacturing the elastic wave device 101 illustrated in FIG. 9 will be described with reference to FIG. 10A to FIG. 10D. First, as illustrated in FIG. 10A, the first electrically conductive film 141, the first dielectric layer 115, and the second dielectric layer 116 are formed on the piezoelectric substrate 110. The electrode fingers 112a and 113a of the IDT electrode 111 are formed from the first electrically conductive film 141. Thereafter, as illustrated in FIG. 10B, parts of the first dielectric layer 115 and the second dielectric layer 116 are removed so that parts of the first electrically conductive film 141 are exposed, and openings 125 are formed above the piezoelectric substrate 110. Subsequently, as illustrated in FIG. 10C, the second electrically conductive films 142 are formed in the openings 125 above the piezoelectric substrate 110. At this time, the second electrically conductive film 142 is stacked on the first electrically conductive film 141. The busbars 112b and 113b, the wiring 114, and the pad 120 are formed from the multilayer body of the first electrically conductive film 141 and second electrically conductive film 142. Then, as illustrated in FIG. 10D, the under bump metal 118 is formed on the second electrically conductive film 142 defining the pad 120. In this regard, the surface of the second electrically conductive film 142 in the vicinity of a contact region C between the second electrically conductive film 142 and the under bump metal 118 is exposed to air.
FIG. 11 is a diagram illustrating an electronic component 102 including the elastic wave device 101 illustrated in FIG. 9. The electronic component 102 includes the elastic wave device 101 and further includes a mounting substrate 131, solder 139, and an insulating resin 132. The electronic component 102 is produced by bonding the elastic wave device 101 and the mounting substrate 131 by using the solder 139 and, thereafter, forming the insulating resin 132 so as to cover the mounting substrate 131 and the elastic wave device 101.
In order to bond the elastic wave device 101 by using the solder 139, a solder paste is used as a bonding agent. However, since the solder paste contains flux, the second electrically conductive film 142 may corrode in the case of contact between the flux and the second electrically conductive film 142. In particular, in the case where Al (aluminum) is used as the material for the second electrically conductive film 142, a chemical reaction may occur between Al and halogen compounds (chlorine ion or the like) in the flux and the second electrically conductive film 142 may corrode. Consequently, the reliability of bonding between the elastic wave device 101 and the mounting substrate 131 may decrease.